trimming podcasts in quicktime

June 1, 2009 8:06 PM

I have a podcast (M4A format) that I'd like to trim and save without re-encoding. Is this possible? In Quicktime Pro I can select a time range, trim it, and choose save, but it saves the resulting file as a .MOV file.

Basically I want to grab a chapter of the podcast and have it as a regular audio file. Eventually this will be done in AppleScript.

Is the .MOV simply a wrapper? It looks as though I can change the file extension to M4A and it loads fine. Do I have to manually change the extension each time? What podcast info has to be removed for iTunes to load it as a regular file and not load it into the podcast section?

posted by krunk to computers & internet (7 comments total)

Are you on Windows or Mac? On a Mac, I don't think the extension is as important: more a signal to the user than the apps.

I think m4a is really aac. Mp4box appears to trim that. Setting a start & end time in iTunes & re-encoding might be a quick way to do that, though possibly with some fidelity loss.

If you want it to be in your regular library, you might try dragging a copy into iTunes.
posted by Pronoiac at 1:28 AM on June 2

I'm on a Mac. If I do a Get Info on the resulting .MOV file, it says it's a Quicktime Movie, but the Codecs are AAC, Text, Photo - JPEG, which is right.

Renaming and dragging it iTunes puts it in the Podcast list automatically, but maybe I can strip out some of the files metadata with an AppleScript.
posted by krunk at 5:11 AM on June 2

SoOmetimes I shorten a track by going to the file's Information (in OS X iTunes), then setting an "end time" and finally using the "Save as mp3..." command.
posted by wenestvedt at 10:37 AM on June 2

You could remove the video portion of your current movie - follow the screenshots.

I vaguely remember some iTunes option for deselecting "audiobook" from the file properties. I couldn't speak about its scriptability, though.

This page has an OS X version of mp4box, under "Pre-compiled binaries."
posted by Pronoiac at 1:43 PM on June 2

After you're done trimming in Quicktime Pro, use the Export command instead of save, choosing a name that ends in m4a instead of mov. Pick Movie to Quicktime Movie, select options, deselect video and internet streaming, leaving only audio selected. You'll want to check your sound settings to make sure they're appropriate before you finish exporting.
posted by Izner Myletze at 1:44 PM on June 2

I don't want to re-encode the file (causing loss of quality), which would happen when doing an Export.

I think what I need to do after trimming is Window->Show Movie Properties, then extract the AAC track. Saving that and renaming with the AAC extension seems to work in iTunes.

Now I just need to do this programmatically!

Thanks for the help.
posted by krunk at 4:53 PM on June 2

If your export format (in the sound settings) is Apple Lossless codec, there will be no loss of quality when exporting.
posted by Izner Myletze at 9:05 PM on June 2